Purpose: Cap43 is known as a nickel- and calcium-inducible gene. In the present study, we examined whether 17beta-estradiol (E2) could affect the expression of Cap43 in breast cancer.
Experimental design: Real-time PCR, immunoblotting, and immunocytochemistry were used to examine the expression of Cap43 and estrogen receptor-alpha (ER-alpha) in breast cancer cell lines. MDA-MB-231 and SK-BR-3 cell lines were transfected with ER-alpha cDNA to establish cells overexpressing ER-alpha. Immunohistochemistry was used to evaluate the expression of the Cap43 protein in breast cancer patients (n = 96), and the relationship between Cap43 expression and clinicopathologic findings was examined.
Results: Of the eight cell lines, four expressed higher levels of Cap43 with very low levels of ER-alpha, whereas the other four expressed lower levels of Cap43 with high ER-alpha levels. Treatment with E2 decreased the expression of Cap43 dose-dependently in ER-alpha-positive cell lines but not in ER-alpha-negative lines. Administration of antiestrogens, tamoxifen and ICI 182780, abrogated the E2-induced down-regulation of Cap43. Overexpression of ER-alpha in both ER-alpha-negative cell lines, SK-BR-3 and MDA-MB-231, resulted in down-regulation of Cap43. Immunostaining studies showed a significant correlation between Cap43 expression and the histologic grade of tumors (P = 0.0387). Furthermore, Cap43 expression was inversely correlated with the expression of ER-alpha (P = 0.0374).
Conclusions: E2-induced down-regulation of Cap43 seems to be mediated through ER-alpha-dependent pathways in breast cancer cells both in culture and in patients. Cap43 has potential as a molecular marker to determine the therapeutic efficacy of antiestrogenic anticancer agents in breast cancer.